docs: def _spherical_to_cartesian(cls, coord, center):
          """Spherical to cartesian conversion
          """
          r, theta, phi, r_dot, theta_dot, phi_dot = coord
          x = r * cos(phi) * cos(theta)
          y = r * cos(phi) * sin(theta)
          z = r * sin(phi)
  
          vx = r_dot * x / r - y * theta_dot - z * phi_dot * cos(theta)
          vy = r_dot * y / r + x * theta_dot - z * phi_dot * sin(theta)
          vz = r_dot * z / r + r * phi_dot * cos(phi)
  
          return np.array([x, y, z, vx, vy, vz], dtype=float)